The Synthesis And Characterization Of 3-Substituted Indole Derivatives Under Ultrasound

The investigation of the chemistry of indoles has been, and continues to be, one of the most active areas of heterocyclic chemistry. In particular,3-substituted indole derivatives have received much attention as important building blocks for the synthesis of many natural products and other biologically active compounds. Recently, there are a lot of reports on the synthesis of 3-substituted indoles from indole. In this article, the one-pot synthesis of 3-substituted indole derivatives from indoles, such as bis(indolyl)methane,β-indolylketone,β-indolylalcohol, P-indolylnitro-compound, was reviewed in recent years according to kinds of catalysts used in synthesis of 3-substituted indole derivatives.Ultrasound has been used more and more frequently in organic synthesis in recent three decades. Compared with traditional methods, a great many of organic reactions can be carried out in higher yields, shorter reaction time or milder conditions under ultrasonic irradiation. In the paper, the principle of sonochemitry and some applications in organic synthesis were reviewed.The conjugate addition of indoles with 1,5-diaryl-1,4-pentadien-3-ones catalyzed by three catalysts such as aluminum chloride, iodine andβ-toluenesulfonic acid afforded the corresponding products in moderate yields under ultrasound irradiation at room temperature. The acceleration of ultrasound on the reaction, effect of solvent, addition order, frequency of ultrasound and molar ratio of substrate were showed in the results. And a plausible mechanism was proposed.Synthesis of bis(indolyl)methanes via eletrophilic substitution reactions of indoles with aromatic and ketones catalyzed by silicotungstic acid (SiO2·12WO3·24H2O) was carried out in 50-97% yield within 15-120 min under ultrasound. Compared with traditional methods, this method is more convenient and reactions can be carried out in shorter reaction time and higher yield under ultrasound irradiation. The reaction activities of aromatic aldehydes were higher than aromatic ketones.Synthesis of 2-((1H-indol-3-yl)(aryl)methyl)malononitrile via the Michael addition of indole with various arylmethylenemalononitriles was carried out in 34-97% yields within 1.5-6 h at r.t using anhydrous zinc chloride as the catalyst under ultrasound irradiation. The reaction activities of ethyl a-cyanocinnamates were lower than arylmethylenemalononitriles.